In an example of the related art adopted in the area where the swash plate is connected to the piston in a swash plate type compressor, a recessed ball receiving portion at a shoe is made to contact the ball only at an intermediate position along the direction of the depth of the recessed ball receiving portion, to form a sealed oil reservoir void space next to the ball under the contact position and to form a narrow clearance that opens to the outside next to the ball above the contact position and a through hole formed so as to pass through the circumferential wall of the shoe toward the oil reservoir void space (see Japanese Unexamined Utility Model Publication No. S 54-38913). This structure is considered to facilitate the supply of lubricating oil to the oil reservoir void space and to the narrow clearance and thus improve lubrication at the sliding portions.
In another example of the related art, at a shoe having a semispherical projecting portion, a semispherical convex surface which slides against a semispherical concave portion formed at a piston with a projecting surface of a rotating body resulting from the rotation around the axis of the shoe is formed with a circular arc drawn around a center offset from the axis of the shoe by a specific distance along the direction perpendicular to the axis (see Japanese Unexamined Patent Publication No. 2001-248547). The clearance created between the semispherical convex portion on the top side of the shoe and the semispherical concave portion by adopting this structure allows the lubricating oil to be supplied with ease to achieve an improvement in the lubrication at the sliding portions.
In the art disclosed in Japanese Unexamined Utility Model Publication No. S 54-38,913 mentioned above, gaps (i.e., the oil reservoir void space and the narrow clearance) are formed between the ball and the recessed ball receiving portion by allowing the recessed ball receiving portion to have a specific curvature which is different from that of a perfect sphere, as illustrated in FIGS. 2 to 4 in this publication 1. In the art disclosed in Japanese Unexamined Patent Publication No. 2001-248547, on the other hand, the void where the lubricating oil is collected is formed by adjusting the curvatures of both the shoe and the semispherical concave portion to predetermined degrees. However, there is a problem in that it is difficult to form a shoe pocket that is equivalent to the recessed ball receiving portion or the semispherical concave portion described above and it therefore necessitates considerable technical expertise and high production costs to form the shoe pocket with an adjusted curvature such as that described above in reference to the related art.
Accordingly, an object of the present invention is to improve the lubrication between the shoe and the shoe pocket without necessitating a complicated forming process.